Chlamydia trachomatis is the most common sexually-transmitted bacterial pathogen worldwide, causing millions of new infections each year. These infections all too frequently result in serious sequelae in women, including pelvic inflammatory disease, infertility, ectopic pregnancy, and chronic pelvic pain. Although screening programs can reduce the prevalence of chlamydial infections and their complications, primary prevention programs are needed. The use of topical microbicides has been recognized as a productive approach for the prevention of chlamydial infections and STD's in general. Chlamydiae are obligate intracellular bacteria which can only grow within eukaryotic cells. Infectious elementary bodies are found in sexual secretions and are adapted for survival in this environment. The organisms are only extracellular for a brief period of their life cycle, but this extra cellular phase is essential for their transmission from person to person. It is during this brief time that Chlamydia are amenable to killing by topical microbicides. The overall goal of this proposal is to evaluate various topical microbicides for their activity against C. trachomatis. This includes: 1. Providing purified C. trachomatis organisms and performing microbiological and DNA amplification methods of chlamydial detection 2. Performing in vitro minimum cidal concentration (MCC) assays with developed or novel antimicrobial compounds and with excipients to determine their activity against C. trachomatis, and 3. assessing the mode of action of previously identified active compounds on C. trachomatis. The Chlamydia Core will provide purified organisms and highly specialized microbiological detection methods for Chlamydia, materials and techniques available in only a few laboratories in the United States. In addition, the Chlamydia Core will carry out MCC assays with various microbicides against C. trachomatis, utilizing our unique expertise with this highly specialized test. Finally, we will examine the mode of action of several microbicides on this organism, providing the first information about how these microbicides exert their anti-chlamydial effects.